This

This -> Object

Parámetros	Tipo		Descripción
Resultado	Object	←	Current element or object

Descripción

The This command returns a reference to the currently processed object.

En la mayoría de los casos, el valor de This está determinado por cómo se llama una función. No se puede definir por asignación durante la ejecución, y puede ser diferente cada vez que se llame a la función.

This command can be used in different contexts, described below. Within these contexts, you will access object/collection element properties or entity attributes through This.<propertyPath>. For example, This.name or This.employer.lastName are valid pathes to object, element or entity properties.

In any other context, the command returns Null.

Función de clase

Cuando se utiliza una función constructora de clase (con la función new()), su This está vinculado al nuevo objeto que se está construyendo.

//Class: ob

Class Constructor  

 // Create properties on This as
 // desired by assigning to them

 This.a:=42

// en un método 4D  
$o:=cs.ob.new()
$val:=$o.a //42

Al llamar a la superclase del constructor en un constructor utilizando la palabra clave Super, tenga en cuenta que This no debe ser llamado antes del constructor de la superclase, de lo contrario se genera un error. See this example.

En todos los casos, This se refiere al objeto sobre el que se ha llamado el método, como si el método fuera una función del objeto.

//Class: ob

Function f() : Integer
 return This.a+This.b

Entonces puede escribir en un método proyecto:

$o:=cs.ob.new()
$o.a:=5
$o.b:=3
$val:=$o.f() //8

En este ejemplo, el objeto asignado a la variable $o no tiene su propia propiedad f, la hereda de su clase. Como f es llamado como un método de $o, su This se refiere a $o.

Objeto fórmula

In the context of the execution of a formula object created by the Formula or Formula from string commands, This returns a reference to the object currently processed by the formula.

For example, you want to use a project method as a formula encapsulated in an object:

 var $person : Object := New object
 $person.firstName:="John"
 $person.lastName:="Smith"
 $person.greeting:=Formula(Greeting)
 $g:=$person.greeting("hello") // returns "hello John Smith"
 $g:=$person.greeting("hi") // returns "hi John Smith"

With the Greeting project method:

 #DECLARE($greeting : Text) : Text
 return $greeting+" "+This.firstName+" "+This.lastName

List box

In the context of a list box associated to a collection or an entity selection, during the On Display Detail or the On Data Change events, This returns a reference to the collection element or entity accessed by the list box to display the current row.

nota

If you use a collection of scalar values in a list box, 4D creates an object for each element with a single value property. Thus, the element value is returned by the This.value non-assignable expression.

Ejemplo 1

A collection of objects, each with this structure:

{  
"ID": 1234
"name": "Xavier",  
"revenues": 47300,  
"employees": [  
             "Allan",  
             "Bob", 
             "Charlie"  
            ] 
},{  
"ID": 2563
"name": "Carla",  
"revenues": 55000,  
"isFemale": true
"employees": [  
             "Igor",  
             "Jane"  
            ] 
},...
 

In the list box, each column refers to one of the properties of the object, either directly (This.name), indirectly (This.employees.length), or through an expression (getPicture) in which can be used directly. The list box looks like:

The GetPicture project method is automatically executed during the On display detail event:

  //GetPicture Method
 #DECLARE -> $genderPict : Picture
 If(This.isFemale)
    $genderPict:=Form.genericFemaleImage
 Else
    $genderPict:=Form.genericMaleImage
 End if

Once the form is executed, you can see the result:

Ejemplo 2

You want to display entities from the following structure in a list box:

You build a list box of the "Collection or entity selection" type with the following definition:

Note que:

• This.ID, This.Title and This.Date directly refers to the corresponding attributes in the ds.Event dataclass.
• This.meetings is a related attribute (based upon the One To Many relation name) that returns an entity selection of the ds.Meeting dataclass.
• Form.eventList is the entity selection that is attached to the list box. The initialization code can be put in the on load form event:

 Case of  
    :(Form event code=On Load)  
       Form.eventList:=ds.Event.all() //returns an entity selection with all entities  
 End case  

Once the form is executed, the list box is automatically filled with the entity selection:

Ver también

Self
Super